Technical Abstract:
Studies conducted in Arizona during 2002-03 evaluated the use of remotely-sensed surrogates of basal crop coefficient (Kcbs) for estimating cotton evapotranspiration (ET) and irrigation scheduling. Main treatments included two scheduling approaches based on the FAO-56 dual crop coefficient procedures that differed only in the method used for Kcb. One used Kcbs derived locally following FAO-56 guidelines. Another used Kcbs based on ground-measured normalized difference vegetation index (NDVI) and a previously defined relationship between Kcb and NDVI for cotton. Added treatments (3 plant densities, 2 nitrogen levels) created conditions that altered cotton ET patterns. Results for 2002 indicated that the FAO Kcb provided appropriate irrigation scheduling for standard and sparse plant densities. However, it underestimated crop ET and, hence, irrigation requirements for a dense cotton planting. Results also revealed that an initial Kcb-NDVI relation, developed for a different cultivar and row orientation than those used in the present experiments, inadequately estimated ET for all treatments. Thus, a new relation was developed from 2002 data, and subsequently used to schedule irrigations for 2003. Results for 2003 inidicate that NDVI can provide feedback for adjusting Kcb to variations in cultural and edaphic conditions and may result in more timely and efficient irrigations.